I am
looking for a device to run Libreelec on, in either a dedicated mode or through
dual boot, and it would need to play 4K flawlessly, pass-through any 5.1
surround stream to my receiver and have a 1000 Mb/s (GigE) Ethernet connection.

I have been browsing through this forum and other forums as well (like the Kodi
forum) and I have been checking out loads of reviews from various Kodi boxes
but I am a bit lost at this point.

I know that everybody is pretty happy with / excited about the ODROID C2 setups
but isn’t this particular system getting a bit outdated? I think someone
mentioned a new Kodi version coming up in near future that is in need of faster
hardware than the 905* CPU? I would like to buy a device which I will be able
to enjoy for a couple of years...

And while
the ODROID itself is not all that expensive, adding a case, power adapter, 8Gb
EMMC drive, Bluetooth module and a good air mouse will raise the price round
about 100 euro’s.For less than that I could get a random brand 4K Kodi Android
box from China with the 912 CPU, like for example the pretty popular 92X, which
has good reviews and benchmarking by the way. These boxes include 2 or 3 Gb of
RAM, 16 or 32 Gb of storage and a remote control.

So, the big
question is: should I go for a ODROID C2 setup and is it future proof or should
I go for a 912 box, and if so, which ones do you prefer / think are the best
ones for a dual boot Libreelec setup

I would like to thank you all in advance for your thoughts on the matter!

Well ODROID C2 can decode 4k HEVC content with ease but keep in mind 4k without HDR is useless because most of 4k content available today are paired with HDR and has wider color gamuts which s905 soc can't decode correctly and the result is washed out colors. s905x/D soc can't output true 10bit colors depth and s912 doesn't support officially by libreelec. if you need true 4k HDR whether you should wait for new Amlogic soc or buy Apple tv 4k.

So.... When I take a look here (kodi forum), it says under "Q. I basically
want a HD Audio capable (inc. Atmos & DTS:X) 4K HDR10 Kodi media player
that just works with minimal hassles ?" that "AMLogic
S905X, S905D and S912 devices running DIY LibreELEC Kodi Krypton" are recommended.

Special mention for S912 devices like the MINIX U9-H because it also has
Gigabit LAN... (good for 4K streaming).

On the forum there are plenty of users running an S912 device with Libreelec,
so, why shouldn’t I?

(Kind of) new question arises though:

The MINIX U9-H must be a good box (also gets nice reviews).

Are there other options like the X92, X96 Pro or the Beelink G1 Ultimate?

The S912 is less well supported by Linux. It is currently using a cludged Android Kernel which will slowly be forced out by upstream Kodi changes that are coming down the tracks. The s905 chips will be more likely to survive these changes in better shape since it uses a more well established Mali GPU. Coupled to this is the fact that the S905 chips are better supported by AMLogic themselves. The only real advantage that the S912 has over the S905 is its gigabit Lan.

At the moment CoreElec supports S912 chips well, but it has been predicted by the developer team that this will degrade over time as Kodi forces changes to the code.

I believe that none of these boards do 4K HDR correctly since they are bottlenecked by the HDMI port, but I could be wrong on this since its a complex area. For me its a none issue.

If and when Kodi makes my S912 card unusable I will migrate to one of the cheap Intel PC boxes such as the Vorke V1+. The whole field of Android boxes is to much in flux and hardware becomes redundant far to quickly for my taste.

Its always going to be a pony race with these boxes with new chips coming along fragmenting the ecosystem and stretching the development teams thinner and thinner, meaning worse support for all but the lucky "latest" designs rolling down the tracks.

VIM2. I got it because it has a supported Sat dTV board. However when the cost of a sat board, power supply and various other bits are taken into account it worked out at around €100.00. If I were to do it over again I would have gone with the MeCool KIII or KII which does there same job in a nicer package. I was sucked in by claims of excellent Linux support which simply wasn't real with the Khadas VIM2.

Still, as I said if I had the decision to make again it would be for the Vorke V1+ at €140.00 with an external SAT>IP box for sat duties.Not much help to your use case I know, but I would be very cautious about going down the S912 path for what in reality will turn out to be no better performance than any of the S905 options.

So... I've done a lot of
reading and researching and according to the specs the 905x chipset should be
able to handle 4K HDR as well as the 912...

Can anyone confirm that?

When the 905x is an option
I could go for the Minix U1 (with Gigabit Ethernet).

Alternative for me would be
the Minix U9-H which is superior to the U1 on the Android platform. Many users
have succeeded in a dual boot with Libreelec on that particular device. However
it is more expensive than the U1.

Witch of the two would be
the best for pure Kodi use?

Oh, and the Minix A2 airmouse/keyboard is usable with Libreelec as well, correct?

Well as far as HDR is your concern none of libreelec supported Amlogic socs can produce true HDR video nor kodi krypton is ready for that. HDR formats composed of many different parts, per pixel brightness metadata, wider color gamuts and more colors(aka 10,12 bits colors ) In other words, they're brighter and more colorful. none of libreelec supported Amlogic socs can do all aspect of HDR at the same time for example S905x soc you mentioned above output 8bits colors instead of 10 and produce fake HDR.

As far as i know Minix U1 has outdated S905 soc not the x variant. which can not decode HDR colors correctly and the result are washed out colors. you should buy tv box with S905X/D soc also S905X doesn't have Gigabit Ethernet. the S905X/D has newer VPU which can decode VP9 videos too.